Onan Genset Won't pump raw water

1990 Onan with 202M11 raw water pump. Quit pushing water. New impeller, old was torn, not wrecked. New impeller, will not lift water to the pump. Sea cock is clean, new hose on intake and raw water system last year. Clamps tight. I can see the impeller moving around with both discharge ant intake hoses off. No instructions. Back filled the system from the exhaust cooling hose to prime it (although the lift is less than a foot) nada. She will not pull water.
Sounds like an air leak and we've run it all summer with zero issues. Can the pump housing be cracked, allowing air? Baffled.

One of the things I do after working on the water pump, is to remove the highest hose on the pump and fill the pump with water. I let it sit for a while and then top it up before reinstalling the hose. I find the pump seals better with a wet impeller, especially if there is significant lift to from sea level to the pump.

Ted

Try pulling the hose off of the seacock and raise the hose above the deck level. Fill the hose with water from a dockside water connection to prime the pump. Start the generator and check for water flow and if established, shut down and connect the hose to the seacock. Restart and verify flow.

James

Have you checked the impeller pump housing for wear?

Is it a Globe run dry impeller (the blue ones)? I've tried those on several different engines, not one of them worked. Switched back to the black neoprene type, the pumps all worked fine. Something about the rubber compound in the blue ones causes them not to seal. They might work in a brand new pump, but not in one with some wear on it.

The old way is to grease the housing and inside cover with waterproof grease. The grease helps seal the impeller to the housing and greatly increases suction. It also protect the impeller ends from getting too hot while waiting for the water. Once too hot, the ends become hard and don't work as well.
I pull my impellers once or twice a year and regrease the housing. If they don't have cracks or hard ends, I put them back in. I get about 500 hours out of my impellers. 2 Detroits, and Onan and Perkins.

Could be pieces of the old impeller blocking the cooler. Blow backwards with your mouth. Collect the pieces, you will be impressed quantity of rubber pieces.

A few times I bought new impellers for Onans and other engines that would not prime. Measured new impeller with dial calipers and found the new one was shorter than the old one!! Not by much (maybe 0.010") but that was enough for a leak path past impeller. I could tell this by blowing through pump with impeller installed. Could blow right through it. Sourced an impeller from another vendor (calipers in hand) and found one with the right length. Pump then worked.

Note that lots of Onan/Kubota pumps are driven by injection pump that only runs 900 rpm. Makes priming more critical.

If cover plate is worn, that will make it worse. Cover plate can be re-surfaced on a lathe or mill to get it back to being flat.

If whole pump is worn, may be a new pump in your future.

Best test is to blow through pump and see how much air goes through. Healthy pump only a little air will go through.

I do hope you bought a couple of the correct impellers.
Cover plates can be turned over.
Lathe or mill time costs more than just buying a new cover.

MacPhid said:

Try pulling the hose off of the seacock and raise the hose above the deck level. Fill the hose with water from a dockside water connection to prime the pump. Start the generator and check for water flow and if established, shut down and connect the hose to the seacock. Restart and verify flow.

James

Click to expand...

Good suggestion. However if you can, lower the hose below waterline and turn on the sea cock. You should have a lot of water. Now proceed with the above.

I have in the past had the intake plugged with kelp. So trace your water flow starting with the seacock.

Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!

NightCrawler said:

Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!

Click to expand...

Try here:

http://m.depcopump.com/?url=http://www.depcopump.com/&utm_referrer=http://www.google.com/#3033

NightCrawler said:

May have to find a machine shop and at least get the wear plate to cozy up with the impeller.
Thank you all!

Click to expand...

Turn the face plate over. Put the outside facing into the pump.

OldDan1943 said:

Turn the face plate over. Put the outside facing into the pump.

Click to expand...

Some pumps have an oring seal in the face plate to prevent that.

Lot to be said for having a spare pump and rebuilding the other at a time and place of your choosing.

Ted

Had the same happen to the sherwood pump on our genset after I changed an impeller.
Location of pump was a blood letting event every time so removed the pump and blanked of the hole.
Installed an MD30 240v electric pump at an easy accessible spot and that's working better than ever , no impellers to wear out and no more blood letting.
Got near 1000 hours on it now,

https://www.ebay.com.au/itm/MD-30-M...057207?hash=item2cbe49a037:g:NdwAAOSwKb5amlAE

Simi 60 said:

Had the same happen to the sherwood pump on our genset after I changed an impeller.
Location of pump was a blood letting event every time so removed the pump and blanked of the hole.
Installed an MD30 240v electric pump at an easy accessible spot and that's working better than ever , no impellers to wear out and no more blood letting.
Got near 1000 hours on it now,

https://www.ebay.com.au/itm/MD-30-M...057207?hash=item2cbe49a037:g:NdwAAOSwKb5amlAE

Click to expand...

Seriously considered this. The existing pump is rated 11gpm. Is the fish tank pump near those numbers.

Did finally have luck finding a new pump. Local team at Specialized Mechanical Services in Wilmington scored one. Should be here today.

NightCrawler said:

Seriously considered this. The existing pump is rated 11gpm. Is the fish tank pump near those numbers.

Click to expand...

Our gennie spins @ 1500rpm so puts out less

They do make larger models, md40 , md55, md70

NightCrawler said:

Wow. Some great answers! Done all of the above. Yeah, the blue impellers suck. My macerator ate one in less than a dozen cycles.

Pulled the Onan pump (this should be an Olympic event) and I'm finding a badly worn face plate. And even though the impeller is a perfect match to one that worked, it seems a tad loose in the casting at the fully extended part. No pumps on-line. The impeller does not extend out of the casting. It's dead even. May have to find a machine shop and at least get the wear plate to cozy up with the impeller.

Thank you all!

Click to expand...

Can you flip the face plate over and provide a NEW surface to mate with the impeller. This, along with greasing the mating surface, sometimes makes the difference.

Our 1989 Onan Genst developed the same problem.....midway through a Medd cruise! A new impeller did not resolve the issue, and our faceplate showed considerable wear. We ended up ordering a new pump, and it's worked perfectly since(7 years now). I've read several blogs on this issue, and the idea of a stand-alone 230vAC pump, powered by the genset once up to speed, or a 12vDC pump on a separate switch, sound like really good advice. It's on our list of things to do, but for now.....if it ain't broke, don't fix it!

Connected with Specialized Mechanical Services
http://specializedmechanical.com/
In Wilmington NC. Had a new pump overnight. Awesome service!!! She's working great!

The owner of SMS came to my boat to help diagnose a dampner plate issue. The engine shop across the street couldn't make it that day so Mr Hank Hinkley who ran the marina where I was suggested SMS. SMS owner (cant find his card right now)came right after lunch and stayed for over 2 hours. We chatted up Lehmans...he was as knowledgeable about them as anyone else I have ever spoken to or read.


After 2 hours of runs and tests...and unable to duplicate symptoms....he said he thought it could be a dampner and agreed with 2 other marine engineers that running it till failure shouldn't be an issue. I made it over 500 miles, 16 miles from my home dock before it quit. Towed myself home the next day with the assistance towboat I ran. Good deal for me to reapair at my leisure and home dock.



Even after the 2 hrs of diagnosing and lots of free knowledge and advice...he packed up and refused payment....what a guy! Took care of him anyway as he was worth staying on his good side.


Would recommend SMS anytime...

How many hours were on the original pump? Are people getting 2000 hours plus from their onan pumps?

Onan genset raw water pump failure

We own a 49 foot Albin Tri-cabin trawler in the PNW with a 1985 7kw Onan genset with 2800 hours on it. Days before you all posted this thread the raw water pump in our genset quit pumping water. Jim replaced the damaged impeller, the pump still did not pump raw water. He tested the thru-hull fitting by back-flushing, no blockage was found. With closer inspection and after reading this thread, Jim realized that wear on the cast bronze end-plate might be excessive enough to cause the problem. He cut a piece of stainless steel to reface the cast bronze end-plate. He could not flip the end-plate because of the casting on the exterior. Unfortunately, the fabricated stainless steel plate did not fix the pumping problem. Jim was not going to be defeated by this simple pump... he removed the pump to determine why it wasn't working. He found the end of the cam inside the pump housing was completely worn away. Jim researched online to find a replacement cam for the pump and found the replacement cam through a parts supplier specializing in obsolete and discontinued pump parts. While looking online he did find replacement pumps for around $500! No Way! He ordered and installed the cam, and reinstalled the pump yesterday, and viola', it worked instantly and was less expensive than the blue Mandalorian cookies in Chapter 12! Thank you for sharing your boating experiences with all of us on Trawler Forum, it has been helpful!